1. Field of the Invention
This invention relates to electric arc furnaces. More specifically it relates to electric arc furnaces in which at least one of the electrodes has an axial opening of appropriate size so that a gas, such as argon, may be introduced into the interior of the arc at an appropriate rate to produce a stabilized, extended arc.
2. Related Prior Art
In an article on "Arc-furnace Melting" by J. A. Charles and A. G. Cowen which was published on Feb. 12, 1960 in Iron and Coal Trades Review (pp. 353-358), the authors describe the feeding of argon through hollow electrodes in an arc furnace used for melting. The operation is compared with the use of solid electrodes and identical conditions apparently including electrode spacing is used as with the solid electrodes. While certain improvements were noted with argon, no attempt was made to produce an extended arc.
A later article (J. Ravenscroft "Electrical Review" pp. 413-418, Sept. 14, 1962) describes the testing of argon introduction through electrode openings in a 5 ton arc furnace. The authors conclude "As shown from the results, furnace performance, as assessed by melting rate, electricity consumption to clearmelt, and electrode consumption, was not improved by using argon during melting on the 5 ton furnace." . . . "There appears to be no practical application for argon in the production furnace, because the increase in arc power which results from an increase of electrical conductivity in the arcs can easily be attained in practice (if desired) by increasing the current settings of the electrode regulator."
U.S. Pat. No. 3,783,167 discloses a cumbersome mechanical device design to produce an extended arc zone by moving an electrode or a plasma gun in a closed path so that the resultant arc with a second annular electrode would be moved into a greater area. In addition to being cumbersome and difficult to maneuver, this equipment has proven to be quite inefficient as a heating or melting device.
U.S. Pat. No. 3,834,895 shows a process using a plasma arc furnace. A gas such as argon is fed into the furnace through an annular passageway surrounding either the electrode or a hopper feeding particulate material into the plasma. In this case, particulate iron-bearing material is dropped into the plasma from a hopper situated immediately above the furnace. The patentee stresses as novel the feature of collecting the melted iron at the bottom of the furnace and removing it in a molten form.
U.S. Pat. No. 2,909,422 uses a hollow electrode in an arc furnace to introduce inert gases, such as argon, to reduce hydrogen pickup, to minimize updraft in the hollow electrode and to reduce the heating period of the furnace. Patentee states "The stream of gas material leaving the bore of the furnace electrode impinges directly upon the surface of the melt, and its velocity produces a stirring or agitating effect in the melt region under the electrode, thereby shortening the reaction time between the melt ingredients and the slag, such as in the case of steel melting, and considerably shortening the refinement period." . . . "By supplying argon through the electrode bore, the moisture in the furnace atmosphere is displaced in the arcing region, which being the hottest part of the furnace is the most likely place for the hydrogen transfer mechanism to occur. An increased rate of argon flow will naturally displace more moisture laden air from the arcing region and consequently will be more likely to prevent the incorporation of hydrogen in the melt."
U.S. Pat. No. 3,105,864 discloses an electric arc furnace having an electrode with an axial opening and an outer coating on the electrode of higher melting point than the remainder of electrode so that when gas is passed through the axial opening the tip of the opening will wear into an enlarged tip or cone at the exit end of the electrode. Patentee is obviously unaware of the possibility of stabilizing and extending the arc by controlling the rate of gas flow and the linear velocity of gas passing through the opening.